FIG. 1 shows a conventional semiconductor laser apparatus driving system disclosed in for example, the official gazette of Unexamined Japanese Patent Publication No. SHO 60-263349. The driving system comprises a beam emitting section 1 a beam receiving section 2 and a printed circuit board 3. The beam emitting section 1 comprises a metallic base plate 4 on which a header 5 acting as a heat sink is mounted. A semiconductor laser array 6 including two semiconductor laser beam sources is mounted on the planar top surface of the header 5. The metallic base plate 4 has a center aperture 4a therein into which a columnar condenser lens 7 is fitted. Three first stems 8, one of which is not shown, are connected to the respective semiconductor laser beam sources of the semiconductor laser array 6 by connecting lines (not shown). The first stems 8 extend through apertures 9a formed in the base plate 4 and filled with glass filler 9 project from the rear surface of the base plate 4. The first stems 8 are secured to the printed circuit board 3. A package 10 has a center aperture 10a therein which is closed with a glass plate 11 bonded to it. The package 10 is secured to the metallic base plate 4 to cover the header 5. The two semiconductor laser beam sources of the semiconductor laser array 6 emit forward beams 12a and 12b and backward beams 13a and 13b. respectively. The forward beams 12a and 12b are directed onto an information recording medium (not shown) for recording or recovering information. As will be stated later, the backward beams 13a and 13b are used for controlling the forward beams 12a and 12b.
The beam receiving section 2 comprises a pair of photodetectors 15a and 15b embedded in a transparent block 14. Out of opposite ends of the transparent block 14, three second stems 16, one of which is not shown, project. The second stems 16 have their inner ends connected to the photodetectors 15a and 15b within the transparent block 14, and have their outer ends attached to the printed circuit board 3.
The printed circuit board 3 has an aperture 3a extending through it which corresponds to the center aperture 4a in the metallic base plate 4.
The photodetectors 15a and 15b of the beam receiving section 2 are located in a position corresponding to the center aperture 4a in the metallic base plate 4 of the beam emitting section 1 and the aperture 3a in the printed circuit board 3. The backward beams 13a and 13b pass through the columnar condenser lens 7 and are focused onto the photodetectors 15a and 15b, respectively. Thus, the control of the forward beams 12a and 12b can be effected by operating driver circuits (not shown for the respective semiconductor laser beam sources by means of output signals from the photodetectors 15a and 15b receiving the backward beams 13a and 13b.
The conventional semiconductor laser apparatus driving system as above stated needs the condenser lens 7 for condensing the backward beams 13a and 13b to focus on the respective photodetectors 15a and 15b, and it is very difficult to dispose the condenser lens 7 within a small inner space of the package 10, and, therefore, it lacks mass-producibility.
Accordingly, the object of the present invention is to provide a mass-producible semiconductor laser apparatus driving system which is free of the above-stated problem by avoiding positioning of a condenser lens within a limited inner space of a package.